Radiocircuits



Aug. 7, 1928. 1,679,347

- R. BELL RADIOCIRGUIT-S Filed Sept.' '7, 1926 2 Sheets-Sheet l Millilillmll H I H mini} INVENTDH.

Aug. 7, 1928. 1,679,347

R. BELL RADIOCIRCUI TS Filed Sept; 7, 1926 2 Sheets-Sheet 2 INVENTDH.

Patented Aug. 7, 1928.

NITED STATES ROBERT BELL, OF HANOVER, ONTARIO, CANADA.

' RADIOCIRGUITS.

Application filed September 7, 1926. Serial No. 134,018.

This invention relates to radio circuits employing one or more stages of tuned radio frequency amplification. The tubes employed in such circuits are, unless some remedy is provided, liable to oscillate with the resulting production of squeals and howls. I have found by experiment that a great deal of the trouble is due to capacity coupling between the primary and secondary coils of the transformers employed, and my object is to stabilize a set employing tuned radio frequency amplification in such a manner to prevent the oscillations referred to.

I attain my object in a manner capable of several modifications.

In the simplest form I position close to or within the transformer a disk of non-magnetic metal, which disk is capable of adjustment to or from the primary or secondary of the coil. As a modification, a coil may be employed which is not electrically connected with any part of the circuit. In a modified form, to overcome the mechanical difiiculties of adjusting the positions of the metal disks, I may connect the disk with the grid circuit of the preceding tube in the set, and in the connection place a small variable condenser. So too in the modification in which I employ a coil, instead of the metal disk, the coil may be connected with the grid circuit of the preceding tube as described, and a variable disk may be employed connected with the grid circuit of the preceding tube without using the variable condenser in the connection. In a yet further modification, both the coil and a stationary disk may be employed electrically connected with the grid circuit of the preceding tube, a variable condenser being included in the connection.

The invention is illustrated in the accompanying drawings in which Figs. 1, 2, 3, 4 and 5 are circuit'diagrams showing circuits provided with my improved stabilizing arrangements.

Fig. 6 is a diagrammatic showing of the structural arrangement of a modification of my invention.

The circuits are of ordinary type and need no special description.

Referring to Fig. 1, it will be noted that metal disks 1 are located adjacent the transformers. If the transformer windings are supported on cylindrical cores, the metal disks will be adjustably mounted to move into or out of the core, preferably adjacent the secondary of the transformer.

In Fig. 2 the disks are shown as electrically connected in each case with the grid circuit of the preceding tube. The positions of the disks being adjustable, no variable condensers are employed in the connections.

In Fig. 3 I show the same arrangement including a variable condenser in the connection between the disk and the grid circuit.

In Fig. 4 I show a coil substituted for the disk and positioned adjacent the ground end of thetransformer coils, a. variable condenser being employed in the connection between the coil and the grid of the preceding tube.

In Fig. 5 I show both a coil and a stationary disk connected with the grid circuit of the preceding tube, a variable condenser being provided in the connection.

I have found, if a set be stabilized for the lower wave lengths, that it is over stabilized for the higher wave lengths. To overcome this difiiculty I arrange the transformer coils below the tuning condensers for the radio frequency circuits so that, as the movable plates of the condensers are withdrawn from between the stationary plates, they will project more or less within the hollow cores of the coils. (See Fig. 6). For the lower wave lengths the set is stabilized by the adjustment of the disks or the stabilizing condensers and, as the tuning condensers are adjusted for the higher wave lengths, the plates project further and further from the hollow cores of the transformer coils and neutralize more or less the stabilizing effect of the stabilizing disks or coils.

.What I claim is:

v An electric circuit arrangement for a radio receiving set employing tuned radio-frequency amplification including a tuning condenser and a radio frequencytransformer wound on a hollow core, comprising means for capacitatively stabilizing the circuit for short wave lengths the transformer being positioned so that as the movable plates of the tuning condenser are withdrawn from between the stationary plates of the condenser they dip into the hollow core of the transformer and more or less neutralize the stabilizing effectof the aforesaid stabilizing means.

Signed at Hanover, Ontario, fourth day of August, 1926.

ROBERT BELL.

Canada, this 

